1. Field of the Invention
The present invention relates to a vacuum evaporator and, more particularly, to a vacuum evaporator capable of slowing the degradation of the sensitivity of a crystal sensor that detects layer thickness.
2. Discussion of the Background
Generally, a vacuum evaporation method is widely used to form an organic layer.
The vacuum evaporation method includes forming a thin layer by installing a source under a vacuum chamber and a substrate for forming a layer on the vacuum chamber. An apparatus for forming an organic thin layer using the vacuum evaporation method includes a vacuum exhaust system connected to the vacuum chamber, and it is configured to maintain the vacuum chamber in a vacuum using the vacuum exhaust system, and then to evaporate a deposition material from at least one source.
The source includes a crucible for receiving an organic thin layer forming material and a heater wound around the crucible to heat the crucible. The heater's temperature is increased to heat the crucible to a predetermined temperature, thereby evaporating the organic thin layer forming material.
A substrate, at which the thin layer is to be formed, is disposed in the vacuum chamber spaced apart from an upper part of the source. A thickness monitor head, which is included at one side of the substrate, includes a crystal sensor for measuring the thickness of the thin layer deposited on the substrate.
The organic thin layer forming material that is evaporated from the source moves to the substrate and then passes through sequential processes such as adsorption, evaporation, re-evaporation and so on, so that it may be solidified on the substrate, thereby forming the thin layer. Here, the thickness of the thin layer may be determined by measuring a layer forming speed using the crystal sensor.
As described above, while the thin layer is deposited on the substrate, the deposition material may also be deposited on a surface of the crystal sensor, thereby applying stress to the crystal sensor, and the crystal sensor may be damaged by the heat used to evaporate the deposition material, which decreases the sensitivity of the crystal sensor. In this case, the thickness of the thin layer deposited on the substrate may not be precisely measured. Furthermore, the crystal sensor's lifetime may decrease, and the vacuum evaporator's maintenance cost may increase.